gate valve or ball valve?

That is not true. Power usage is determined by work done. Less water pumped means less less work done and less power consumed. There is simply nothing wrong with throttling a pump. You will not reduce the life span any meaningfull amount at all.

What is bad for a centrifical pump is dead heading it for long periods of time because inadequate cooling flow is provided. Also, what is bad for a pump is throttling the inlet.

 

Just asking. There is no reason to recirc back to the sump. A valve on the discharge will do what you want. Also, no too many times you would want to "shut off" flow to your sump without turning a pump off.

 

Another question I have is regarding the mag12 pump. It has a 3/4" outlet, but it says that for best flow rates, you are supposed to step it up to 1.5". Anyone know why that is?

 

I always thought that was pretty funny. I mean 1.5" is huge. I run mine on an inch. It is a matter of less restriction and getting the most flow. But who is going to run 1.5 inch pipe or flex on a mag 12. Says the same for a 9.5

 

The return pipe (bulkhead up) that was supplied by the aquarium builder is 1". Seeing the 1.5" would make it a pain with all the fittings. I think I'll just upsize it to 1" and let it go all the way up.

 

Have you taken KW reading of pumps with throttled off outlets? I have. They use the same wattage on any of the magnetic drive pumps as pumps that don't have any restriction on the outlet. You said it yourself that the pump will reduce its lifespan, although it is very hard to quantify " meaningful amount"

Also, danner mag drive pumps don't deal with restrictions like this very well. Other brands such as quiet ones deal with restriction better, like a SCWD.

I had a mag9.5 that lasted less than 2 years when running a scwd on the return. The SCWD is known to reduce gph by around 50% on a mag9 with only a couple feet of head on an in stand sump setup. Running the scwd is exactly the same effect as putting a valve and restricting the output. The housing wore out from increased stress on it. A new impeller did not alleviate the issue, and it would throw the GFCI every time it was plugged in, regardless of the condition of the impeller.

On the same manifold, but without a reducing bushing because the QO3000 with 780 gph uses a bigger outlet, the lower gph rated QO pump actually flowed more water than the 950 gph rated mag9.5. That QO pump used 40 watts compared to 93 of the mag9. While i did not test the longevity, the simple fact that the scwd did not bog the pump down like the scwd bogged the mag9 down tells me that it would last considerably longer than the mag9 if run that way.

Also, the manifold I had used had a tee feeding my recirc skimmer, so had I not had the tee off feeding the skimmer, I bet that mag9 would have failed even sooner.

Yes, throttling the inlet is bad as well.

 

1" is more than adequate.

 

I have monitored pumps and power consumption for 20 years. You will reduce the life span of a pump by pluging it in.

You can't take one pump and do away with the laws of physics. Pumps are pumps. Their job is to move water. How they perform and what they are intended for are design considerations unique to each pump.

Power consumption is also determined by power factor and you can't compare aples to oranges.

Lets compare apples to apples. Ehiem 1260/1262. 635gph/900gph 65w/80w respectively. The only difference between the two is the inlet. Same motor, same impeller, same discharge. Yet by reducing the inlet, they reduce GPH. Reduced GPH = reduced power consumption.

The only thing bad about reducing an inlet is that you run the risk of cavitation. But the engineers at Ehiem are comfortable with their suction head calculations and appearantly do not worry about the cavitation reducing the inlet of the 1260. You can turn a 1260 into a 1262 by simply replacing the inlet. You will get 900 gph and it will cost you 15 more watts.

Every single aquarium pump in use is throttled. There is not one single one being used for free flow. By putting piping in, equipment, head loss...ect. you are throttling the out put of the pump. Cost of doing buisness.

So it does not reduce it's life span by throttling it. It reduces the life span by running it. Water moved = power consumption. Now recircing the sump is of no use. Lets say you buy a 1262 and recirc the equivilant of a 1260 to the sump. 265 gph at 15w 24/7/365. Well you would come up with a total watts for the year of 131,400. 131 kw hours times say .15 cents/kwh.... and that comes to $19.71. Well hell, is that a big deal....not really. But it is a cost, it is a way to reduce power, and it is a way to reduce heat input to the system.

 

ok, so one final question...

If you look at the pic, should my gate valve be at point 1 or point 2? I will go with the recirculation method. My personal feeling would be to put it at point 2, as this is the shortest distance and path of least resistance, so naturally more water would want to travel this way. By controlling the gate valve, I can send more water to the display. Am I right? Or am I wrong? And why?

 

i have a curve ball to throw at you. how about spot 3? (pic attached)
i dont have any argument other then simply its what i am doing with my sump. hopefully someone who knows more will respond, im curious